Most lightweight distribution?

I don't really know a lot about linux as I use mostly windows, but I was asked by a family member to factory reset a very old pc and prepare to simply be able to go to the internet and see netflix.

Using windows would be a waste of pc resources as it won't be using most of its options. I know there are many options, I was thinking of ubuntu because it's the most famous, but what is the most of lightweigh option for this situation?